1. Field of the invention
The invention applies to television cameras, and more particularly to cameras which can film in either of the two most common formats (or H/V aspect ratios), i.e. in a conventional 4/3 format or in the more recent format, used notably for high-definition television, 16/9, H being the horizontal dimension of the image and V its vertical dimension.
The most efficient television cameras have automatic correction devices which process the information from the analysis of an optical reference sight or test pattern from which the measurements and the corresponding necessary corrections are carried out automatically. These corrections are corrections of convergence, contrast, etc.
French patent application no. 81 01287 describes an automatic correction device of this type, and French patent application no. 82 08486 describes an optical sight particularly suitable for the correction of defects in television images, and for their processing by the automatic correction device described in the first patent application referred to above.
Future television cameras are planned which will be able to film in either of the two formats 4/3 and 16/9. To change from one format to the other, the amplitudes of the scanning voltages of the camera tubes are modified.
2. Description of the prior art
The problem is then to have, for each of the two formats used, a sight in the correct format to serve as an absolute reference for automatic adjustment.
To solve this problem, certain cameras have been equipped with a separate rectangular sight for each format. Two solutions have been used for this purpose:
cameras incorporating in the filter holder two diascope devices each equipped with a specific sight have been used;
diascope lenses equipped with two or four sights have also been proposed.
These solutions present many technical difficulties as it is absolutely necessary that the two sights be perfectly aligned on the optical axis (centering and rotation) and identically lit (light level and uniformity) for the automatic correction device to function correctly, whatever the format used. The cost of such a solution is obviously high. In addition a device with a double sight requires a mechanical system to switch sights. Such a device is bulky, heavy, and incompatible with the light lenses intended in particular for reporting cameras; it can therefore not be used for light cameras carried on the shoulder.
The idea of the invention is to construct a single specific sight usable for both possible image formats.
According to the invention, an optical sight for a camera with automatic geometry and convergence correction, constituted by the horizontal and vertical repetition of an elementary motif on which the measurements necessary for corrections are based, is characterised by the fact that, for a bi-format 4/3 and 16/9 camera, the sight includes a central zone formed of n lines of p motifs, used for both formats, two adjacent external horizontal zones of length p elementary motifs and two adjacent external vertical zones of height n elementary motifs, the external horizontal zones being used with the central zone of n.p motifs for the 4/3 format and the vertical zones being used with the central zone of n.p motifs for the 16/9 format, and the diagonals of the sight surfaces used in the two formats being more-or-less equal.
Another object of the invention is a camera equipped with such a sight.